Ink-jet printers print by shooting drops of ink onto a page. The ink is stored in a reservoir and discharged onto the page through nozzles in a printhead. To print an image, the printhead moves back and forth across the page shooting drops as it moves.
A problem with ink-jet printers is that air bubbles can be forced into the nozzles and interfere with the operation of the printhead. Additionally, ink can drool out of the nozzles, dry and clog them. Items such as dirt and paper dust may also collect on the printhead and clog the nozzles.
To address these problems, ink-jet printers typically include caps and service stations. A cap encloses and defines a cavity around the printhead when the printhead is not in use. A service station is a location on the printer where the printhead can be serviced and protected. The cap is usually located in the service station.
The cap helps prevent ink from drying on the printhead by providing a cavity that can be kept moist. Ink is discharged into the cavity and the moisture from the ink keeps it from drying on the printhead.
However, the volume of the cavity can be decreased when the cap encloses the printhead, resulting in a change of pressure within the cavity. If the pressure within the cavity changes, air bubbles can be forced into the printhead's nozzles. Thus, printhead caps are vented to allow the pressure within the cavity to equalize with the pressure outside the cavity so that air bubbles are not forced into the printhead's nozzles.
Previously existing caps have been vented through a pump connected to the cavity. An example of such a cap is disclosed in U.S. Pat. No. 4,853,717 titled "Service Station for Ink-Jet Printer."
Nevertheless, the previously existing pumps, or the tubing associated with the pump, can become clogged with dried ink. When clogged, the cap is not vented, often resulting in printhead damage. Additionally, pumps require moving parts which add undesirable complication and expense.
The invented cap and service station protect and clean an ink-jet printhead without requiring a pump and without venting through a pump. The invented cap is vented to atmosphere but uses capillary action rather than a pump to passively keep the vents from clogging. Accordingly, the cost and complexity of a pump is avoided and the necessary elements for an ink-jet printer are minimized.